The present invention relates generally to devices and methods useful in potting a filter for use in blood processing, such as hemofiltration, hemodialysis, hemodiafiltration, apherisis, hemoconcentration, and hemo-ultrafiltration. More specifically, the devices and methods provide even distribution of potting material at the ends of the filter.
Dialysis has prolonged the lives of patients with acute or chronic renal insufficiency. In hemodialysis, for example, a semi-permeable membrane or filter is used to remove unwanted substances from the blood while adding desirable components by the process of diffusion across the filter. Fluid removal during dialysis is partially determined by (1) the hydrostatic pressure changes, and (2) the dialysis membranes that have differing ultrafiltration coefficients, i.e., fluid removed per millimeters of mercury pressure per minute. The principal dialyzer used in the United States is the hollow fiber or capillary dialyzer. In the hollow fiber or capillary dialyzer, membrane material is spun into fine capillaries and thousands of these capillaries are packed into bundles. Blood flows through the capillaries while dialysate is circulated on the outside of the fiber bundle.
Membranes or filters used in hemofiltration, hemodialysis, hemodiafiltration, apherisis, hemoconcentration, and hemo-ultrafiltration are prepared in a similar fashion. Potting material, such as polyurethane, is used to bond the membrane fibers within the dialyzer housing. However, even distribution of the potting material along the filter capillaries is difficult to achieve.
What is needed are devices and methods that can be used to evenly distribute potting material along the fiber membrane for use during hemofiltration, hemodialysis, hemodiafiltration, apherisis, hemoconcentration, and hemo-ultrafiltration.
The present invention provides devices and methods that allow even distribution of potting material along the ends of the filter fibers for use in blood processing procedures. In one embodiment, the device comprises a cylindrical-shaped housing with an outer surface and a hollow lumen. One hole near one end of the housing communicates between the outer surface and the hollow lumen. A second hole at the other end of the housing also communicates between the outer surface and the hollow lumen. The housing includes a ridge in the outer surface that extends around the first hole and around the second hole. The ridge takes the form of a trough and acts to guide flowable material through the first hole and through the second hole when flowable material flows toward the holes.
In use, the housing is packed with filter fiber membrane in the hollow lumen, and is covered at each end. A containment cover is placed over the trough. The housing is then rotated about an axis that bisects the housing and is perpendicular to the longitudinal axis of the lumen of the housing. A flowable potting material, e.g., polyurethane, is placed on the outer surface of the housing off center about halfway between the first hole and the second hole. As the housing spins, the flowable potting material divides into two portions, such that one portion flows toward the first hole, and a second portion flows toward the second hole. The ridge acts as a backstop behind each hole. The ridge retains the flowable material and guides the flowable material through each of the first and second holes.
The flowable material then passes into the hollow lumen of the housing and distributes between the filter fibers. Centrifugal force impels the flowable potting material toward the ends of the filter fibers until it contacts the ends of the housing. In this manner, flowable potting material is evenly distributed to each end of the housing and filter fibers. The flowable potting material is then allowed to harden by curing, thereby bonding the fibers. The housing and filter fibers are then cut at each end to open the fibers closed by the urethane and to form a smooth surface that will receive and/or pass blood. The filter or dialyzer is completed by attaching a cap on each end of the cylindrical housing.
In another method, the filter fibers are placed in the housing and the trough with a dam feature is filled with urethane. The housing is then spun, forcing the urethane over the dam by centrifugal force into the first and second holes. The urethane then passes into the hollow lumen of the housing and distributes between the filter fibers. After the urethane is allowed to harden and bond the fibers, the ends of the housing and fibers are cut to form a smooth surface and a cap is attached on each end of the housing.
It will be understood that there will be several advantages to using the devices and methods described herein for distribution of potting material. These advantages include (1) ease and efficiency of distributing potting material due to elimination of step of potting in a separate housing, (2) reduced expense of manufacturing, (3) precise control of even distribution of potting material; and (4) elimination of a separately molded component for delivery of the potting material by having a built-in trough.